he he no probs. you don't use target anything on the druid (well maybe mobs)

you need to set the focus on your druid to the lock first using the command
Code:
/focus [target={lock's name}]
and assign it to a macro

or you could just go the name route
e.g.
Code:
/cast [target=player]mod:shift][target=lock,nodead] Regrowth
this will work as follows
* cast regrowth on the druid if shift is held down
* cast regrowth on the lock